Crystal Chemistry, Magnetic and Electrical Properties of La(2-X)BaXNiO4

The series of compositions La2-XBaXNiO4 0 or x or 1.0 was prepared by standard ceramic techniques. All members of the system crystalized with the tetragonal K2NiF4 structure. The ratio of lattice parameters, ca, reached a maximum in the range x 0.5 to 0.6 c increased up to this point while a decreased, and this trend reversed after the maximum was reached. Increase in ca is attributed to a weak Jahn-Teller distortion due to octahedral site low-spin Ni3 ions. Magnetic susceptibilities measured in the temperature range 6 to 300 K and room temperature resistivity measurements showed that with addition of any barium into the system, a significant change was seen in both magnetic and electrical properties. An anomaly in the magnetic susceptibility was seen at 110 K in La2NiO4. This anomaly disappeared and magnetic susceptibility dropped by a factor of at least one-third with addition of barium. With further increases in barium, the susceptibility value did not differ significantly in all Ba-substituted compounds. Room temperature resistivity dropped from 0.14 Ohm-cm for La2NiO4 to 0.05 Ohm-cm for La1.8Ba. 2NiO4 and decreased only slightly thereafter with increasing barium. Semiconducting behavior was observed for all the compounds. Oxygen stoichiometry is suspected to play a critical role in explaining these behaviors. Theses.